In recent years, the circuit line width required for semiconductor devices has been getting narrower with the increase in the degree of integration and capacity of large scale integrated circuits (LSI). These semiconductor devices are manufactured by using an original image pattern (also referred to as a mask or a reticle, and hereinafter referred to as a mask) on which a circuit pattern is formed and by exposing and transferring the pattern onto a wafer using a reduced projection exposure apparatus which is a so-called stepper to form a circuit.
And now, improvement of yield is indispensable for manufacturing LSTs requiring a large manufacturing cost. However, as represented by 1 gigabit class dynamic random access memory (DRAM), patterns constituting the LSI are now on the order of submicrons to nanometers. In recent years, with the miniaturization of dimensions of the LSI pattern formed on a semiconductor wafer, the dimension of a pattern defect to be detected is extremely small. Therefore, higher accuracy of a pattern inspection apparatus is required for inspecting defects of ultrafine patterns transferred onto a semiconductor wafer. Besides, as one of the major factors for lowering the yield, pattern defects of a mask used for exposing and transferring an ultrafine pattern on a semiconductor wafer by a photolithography technique can be mentioned. Accordingly, the accuracy of the pattern inspection apparatus for inspecting defects of the transfer mask used for LSI manufacturing needs to be improved.
As an inspection method, a method of performing an inspection by comparing an optical image obtained by capturing an image of a pattern formed on a sample such as a semiconductor wafer or a lithography mask at a predetermined magnification by using an enlarging optical system with design data or an optical image obtained by capturing an image of the same pattern on a sample is known. For example, as a pattern inspection method, there are a “die to die inspection” of comparing optical image data obtained by capturing images of identical patterns at different places on the same mask each other, and a “die to database inspection” in which drawing data (design pattern data) converted into a device input format to be input by a drawing apparatus at the time of drawing the pattern using CAD data of designed pattern as a mask is input to an inspection apparatus, and design image data (reference image) is generated on the basis of the drawing data, and then the design image data is compared with an optical image obtained by capturing an image of the pattern as measurement data. In the inspection method in such an inspection apparatus, the inspection object substrate is disposed on a stage, and the sample is scanned with the light flux by the movement of the stage, and the inspection is performed. The inspection object substrate is irradiated with a light flux by a light source and an illumination optical system. Light transmitted through or reflected from the inspection object substrate forms an image on the sensor via the optical system. The image captured by the sensor is sent as measurement data to the comparison circuit. In the comparison circuit, after the images are aligned with each other, the measurement data and the reference data are compared according to an appropriate algorithm, and when both of the data do not agree with each other, presence of a pattern defect is determined.
The above-described pattern inspection apparatus acquires an optical image by irradiating an inspection object substrate with a laser beam and capturing a transmission image or a reflection image of the substrate. On the other hand, an inspection apparatus has been developed, which irradiates the inspection object substrate with multi-beams composed of a plurality of electron beams in an array arrangement in which a plurality of rows of beams aligned at the same pitch on a straight line are arranged, and detects secondary electrons corresponding to the respective beams emitted from inspection object substrate to obtain a pattern image. In a pattern inspection apparatus using an electron beam including such multi-beams, secondary electrons are detected by scanning each small area of the inspection object substrate. At this time, the so-called step-and-repeat operation is carried out in which the position of the inspection object substrate is fixed during scanning with a beam, and the position of the inspection object substrate is moved to the next small area after scanning is completed. Since multiple beams can be arranged within a limited area by using multi-beams of array arrangement including a plurality of rows of beam lines each having beams disposed at the same pitch on a straight line, scanning of many small areas can be done at the same time. Therefore, improvement of throughput is expected. However, the settling time (overhead time) until the stage position is stabilized is required for every stage movement in the step-and-repeat operation. Since one scanning range (small area) is small, the number of steps of the stage is enormous in order to scan the entire substrate. Accordingly, time calculated by multiplying the step number by the settling time is generated as unnecessary time not required for scanning. Even when scanning is carried out on the substrate by using multi-beams, there is also a provisional estimate indicating that an unused period of time for scanning generated for one substrate comes up to 80 hours or more, for example.